TRPV4 is a member of the Transient Receptor Potential (TRP) superfamily of cation channels and is activated by heat, demonstrating spontaneous activity at physiological temperatures (Guler et al., 2002. J Neurosci 22: 6408-6414). Consistent with its polymodal activation property TRPV4 is also activated by hypotonicity and physical cell stress/pressure (Strotmann et al., 2000. Nat Cell Biol 2: 695-702), through a mechanism involving phospholipase A2 activation, arachidonic acid and epoxyeicosatrienoic acid generation (Vriens et al., 2004. Proc Natl Acad Sci USA 101:396-401). In addition, amongst other mechanisms proposed, tyrosine kinase activity, as well as protein kinase A and C, may also regulate TRPV4 (Wegierski et al., 2009. J Biol Chem. 284: 2923-33; Fan et al., 2009. J Biol Chem 284: 27884-91).
Heart failure results in the decreased ability of the left ventricle to pump blood into the peripheral circulation as indicated by a reduced ejection fraction and/or left ventricular dilation. This increases the left ventricular end diastolic pressure resulting in enhanced pulmonary blood pressures. This places the septal barrier, which separates the circulatory aqueous environment and the alveolar airspaces of the lung, at risk.
Increased pulmonary pressure results in the flow of fluid from the pulmonary circulation into the alveolar space resulting in lung edema/congestion, as is observed in patients with congestive heart failure.
TRPV4 is expressed in the lung (Delany et al., 2001. Physiol. Genomics 4: 165-174) and its level of expression is up-regulated in individuals with congestive heart failure (Thorneloe et al., 2012. Sci Transl Med 4: 159ra148). TRPV4 has been shown to mediate Ca2+ entry in isolated endothelial cells and in intact lungs (Jian et al., 2009. Am J Respir Cell Mol Biol 38: 386-92). Endothelial cells are responsible for forming the capillary vessels that mediate oxygen/carbon dioxide exchange and contribute to the septal barrier in the lung. Activation of TRPV4 channels results in contraction of endothelial cells in culture and cardiovascular collapse in vivo (Willette et al., 2008. J Pharmacol Exp Ther 325: 466-74), at least partially due to the enhanced filtration at the septal barrier evoking lung edema and hemorrage (Alvarez et al., 2006. Circ Res 99: 988-95). Indeed, filtration at the septal barrier is increased in response to increased vascular and/or airway pressures and this response is dependent on the activity of TRPV4 channels (Jian et al., 2008. Am J Respir Cell Mol Biol 38:386-92). Consistent with these observations, TRPV4 antagonists prevent and resolve pulmonary edema in heart failure models (Thorneloe et al., 2012. Sci Transl Med 4: 159ra148). Overall this suggests a clinical benefit of inhibiting TRPV4 function in the treatment of acute and/or chronic heart failure associated lung congestion.
Additional benefit is suggested in inhibiting TRPV4 function in pulmonary-based pathologies presenting with symptoms including lung edema/congestion, infection, inflammation, pulmonary remodeling and/or altered airway reactivity. A genetic link between TRPV4 and chronic obstructive pulmonary disorder (COPD) has recently been identified (Zhu et al., 2009. Hum Mol Genetics, 18: 2053-62) suggesting potential efficacy for TRPV4 modulation in treatment of COPD with or without coincident emphysema. Enhanced TRPV4 activity is also a key driver in ventilator-induced lung injury (Hamanaka et al., 2007. Am J Physiol 293: L923-32) and it is suggested that TRPV4 activation may underlie pathologies involved in acute respiratory distress syndrome (ARDS), pulmonary fibrosis (Rahaman et al., 2014. J Clin Invest 124: 5225-38), cough (Bonvini et al., 2016 J Allergy Clin Immunol 138: 249-61) and asthma (Liedtke & Simon, 2004. Am J Physiol 287: 269-71). A potential clinical benefit for TRPV4 blockers in the treatment of sinusitis, as well as allergic and non-allergic rhinitis is also supported (Bhargave et al., 2008. Am J Rhinol 22:7-12).
TRPV4 has been shown to be involved in acute lung injury (ALI). Chemical activation of TRPV4 disrupts the alvelor septal blood barrier potentially leading to pulmonary edema (Alvarez et al, Circ Res. 2006 Oct. 27; 99(9):988-95). In animal models, TRPV4 antagonism attenuates lung damage induced by chemical agents and biological toxins such as HCl, chlorine gas, and platelet activating factor (Balakrishna et al., 2014. Am J Physiol Lung Cell Mol Physiol 307: L158-72; Morty et al., 2014. Am J Physiol Lung Cell Mol Physiol 307: L817-21; Yin et al., 2016. Am J Respir Cell Mol Biol 54: 370-83). In addition, TRPV4 is necessary in a process known to cause or worsen ALI in humans (Hamanaka et al, Am J Physiol Lung Cell Mol Physiol. 2007 October; 293(4):L923-32). Overall this suggests a clinical benefit of inhibiting TRPV4 function in the treatment of ARDS and ALI.
Furthermore, TRPV4 has in recent years been implicated in a number of other physiological/pathophysiological processes in which TRPV4 antagonists are likely to provide significant clinical benefit. These include various aspects of pain (Todaka et al., 2004. J Biol Chem 279: 35133-35138; Grant et al., 2007. J Physiol 578: 715-733; Alessandri-Haber et al., 2006. J Neurosci 26: 3864-3874), genetic motor neuron disorders (Auer-Grumbach et al., 2009. Nat Genet. PMID: 20037588; Deng et al., 2009. Nat Genet PMID: 20037587; Landoure et al., 2009. Nat Genet. PMID: 20037586), cardiovascular disease (Earley et al., 2005. Circ Res 97: 1270-9; Yang et al., 2006. Am. J Physiol. 290:L1267-L1276), bone related disorders [including osteoarthritis (Muramatsu et al., 2007. J. Biol. Chem. 282: 32158-67), genetic gain-of function mutations (Krakow et al., 2009. Am J Hum Genet 84: 307-15; Rock et al., 2008 Nat Genet 40: 999-1003) and osteoclast differentiation (Masuyama et al. 2008. Cell Metab 8: 257-65)], itch (Akiyama et al., 2016. J Invest Dermatol 136: 154-60; Chen et al., 2016. J Biol Chem 291: 10252-62), stroke and disorders associated with cerebral edema (Li et al., 2013. Front Cell Neurosci 7: 17; Jie et al., 2015. Front Cell Neurosci 9: 141), inflammatory bowel disorders (Vergnolle, 2014. Biochem Pharmacol 89: 157-61), various diseases of the eye including glaucoma and retinopathy (Monaghan et al., 2015. PloS One 10: e0128359; Jo et al., 2016. Proc Natl Acad Sci USA 113: 3885-90), and metabolic syndrome including obesity and diabetes (Ye et al., 2012. Cell 151: 96-110; Duan et al., 2015. Mol Genet Genomics 290: 1357-65).
Thornelone et al., 2012. Sci Trans Med 4:159ra148; Balakrishna et al., 2014 Am J Physiol Lung Cell Mol Physiol. 307:L158-L172; Hilfiker et al., 2013 ACS Med. Chem. Lett. 4: 293-296; Skerratt et al., 2013 Med. Chem. Commun. 4: 244-251; Everaerts et al., 2010, Proc Natl Acad Sci USA 107: 19084-19089; and Vincent et al., 2009 Biochem Biophys Res Commun 389: 490-494, describe antagonists of TRPV4.
Chronic cough is highly prevalent worldwide and is highly impactful on the quality of life for suffers, with typical cough rates of 10-50 coughs per hour, during waking hours. It is hypothesized that chronic cough reflects a state of neuronal hypersensitivity involving exaggerated spinal and cortical responses to afferent sensory signals in a manner similar to chronic pain. Activation of TRPV4 channels in vivo causes ATP release and triggers afferent sensory signals from the lung through binding of ATP to P2X3 channels, resulting in cough (Bonvini S J, et al., J Allergy Clin Immunol. 2016 July; 138(1):249-261.e12). ATP levels are increased in exhaled breath of patients with diseases associated with cough, for example COPD (Basoglu O K, et al., Chest. 2015 August; 148(2):430-5). Recently a P2X3 antagonist has demonstrated high level efficacy in reducing chronic cough and improving quality of life scores in a phase 2 clinical trial (Abdulqawi R, et al. Lancet. 2015 Mar. 28; 385(9974):1198-1205). These clinical data along with data from pre-clinical models suggests a role for TRPV4 receptors in generating cough. TRPV4 receptors are expressed in airway smooth muscle cells (McAlexander M A, et al., J Pharmacol Exp Ther. 2014 April; 349(1):118-25), in airway epithelial cells (Delany N S, et al., Physiol Genomics. 2001 Jan. 19; 4(3):165-74), and in sensory neurons in the lung, including Ad-fibers from airway specific afferent neurons (Bonvini S J, et al., J Allergy Clin Immunol. 2016 July; 138(1):249-261.e12). Taken together, these data suggest a potential therapeutic role for TRPV4 antagonists in cough; including acute cough, sub-acute cough and chronic cough.